RAYLEIGH-SCATTERING OF MOSSBAUER RADIATION IN ORIENTED FIBERS OF HYDRATED BIOPOLYMERS

The Rayleigh scattering of Mossbauer radiation (RSMR) has been measure d on films of highly oriented hydrated polynucleotides (A-NaDNA) and p olysaccharides (Na-hyaluronate). Both DNA and hyaluronate (HA) have he lical secondary structures with a similar pitch (28.2 Angstrom for A-D NA, and 32.8 Angstrom for Na-HA), but they differ in the basic element s which make up the helices and in the extent of water-biopolymer inte ractions. These differences are responsible for the diverse stiffness of the polymer backbone, and also affect the dynamics of the first hyd ration layers. For both samples the elastic scattering intensity shows a sharp peak at about 2 Angstrom(-1) only for samples oriented with Q parallel to the fibre direction. Its position is close to that of the first maximum in the structure factor of bulk water; it is, however, much narrower than in pure H2O and it is similar to a crystalline Brag g peak. It can be attributed to an ordered structure of water along th e double helices. From the temperature dependence of the elastic inten sity under the peak maximum, the mean square displacement of water oxy gens in the direction parallel to the helices has been deduced. The th ermal diffuse scattering intensity is also peaked at the same Q values of the elastic intensity, indicating the presence of coherent vibrati onal excitations propagating along the ordered water filaments.